Ab initiocalculation of resonant x-ray scattering in manganites

We study the origin of the resonant x-ray signal in manganites and generalize the resonant cross section to the band-structure framework. With ab initio LSDA and $\mathrm{LSDA}+U$ calculations we determine the resonant x-ray spectrum of ${\mathrm{LaMnO}}_3.$ The calculated spectrum and azimuthal angle dependence at the Mn K edge reproduce the measured data without adjustable parameters. The intensity of this signal is directly related to the orthorhombicity of the lattice. We also predict a resonant x-ray signal at the La L edge, caused by the tilting of the ${\mathrm{MnO}}_6$ octahedra. This shows that the resonant x-ray signal in the hard x-ray regime can be understood in terms of the band structure of a material and is sensitive to the fine details of crystal structure.